Apparatus for mapping and coagulating soft tissue in or around body orifices

ABSTRACT

A probe that may be used to create circumferential lesions in body tissue and, in some implementations, may also be used to perform mapping functions. The probe includes a collapsible/expandable structure that supports electrodes or other operative elements against the body tissue.

BACKGROUND OF THE INVENTIONS

1. Field of Inventions

The present inventions relate generally to medical devices that supportone or more diagnostic or therapeutic elements in contact with bodytissue and, more particularly, to medical devices that support one ormore diagnostic or therapeutic elements in contact with bodily orificesor the tissue surrounding such orifices.

2. Description of the Related Art

There are many instances where diagnostic and therapeutic elements mustbe inserted into the body. One instance involves the treatment ofcardiac conditions such as atrial fibrillation and atrial flutter whichlead to an unpleasant, irregular heart beat, called arrhythmia.

Normal sinus rhythm of the heart begins with the sinoatrial node (or “SAnode”) generating an electrical impulse. The impulse usually propagatesuniformly across the right and left atria and the atrial septum to theatrioventricular node (or “AV node”). This propagation causes the atriato contract in an organized way to transport blood from the atria to theventricles, and to provide timed stimulation of the ventricles. The AVnode regulates the propagation delay to the atrioventricular bundle (or“HIS” bundle). This coordination of the electrical activity of the heartcauses atrial systole during ventricular diastole. This, in turn,improves the mechanical function of the heart. Atrial fibrillationoccurs when anatomical obstacles in the heart disrupt the normallyuniform propagation of electrical impulses in the atria. Theseanatomical obstacles (called “conduction blocks”) can cause theelectrical impulse to degenerate into several circular wavelets thatcirculate about the obstacles. These wavelets, called “reentrycircuits,” disrupt the normally uniform activation of the left and rightatria.

Because of a loss of atrioventricular synchrony, the people who sufferfrom atrial fibrillation and flutter also suffer the consequences ofimpaired hemodynamics and loss of cardiac efficiency. They are also atgreater risk of stroke and other thromboembolic complications because ofloss of effective contraction and atrial stasis.

One surgical method of treating atrial fibrillation by interruptingpathways for reentry circuits is the so-called “maze procedure” whichrelies on a prescribed pattern of incisions to anatomically create aconvoluted path, or maze, for electrical propagation within the left andright atria. The incisions direct the electrical impulse from the SAnode along a specified route through all regions of both atria, causinguniform contraction required for normal atrial transport function. Theincisions finally direct the impulse to the AV node to activate theventricles, restoring normal atrioventricular synchrony. The incisionsare also carefully placed to interrupt the conduction routes of the mostcommon reentry circuits. The maze procedure has been found veryeffective in curing atrial fibrillation. However, the maze procedure istechnically difficult to do. It also requires open heart surgery and isvery expensive.

Maze-like procedures have also been developed utilizing catheters whichcan form lesions on the endocardium (the lesions being 1 to 15 cm inlength and of varying shape) to effectively create a maze for electricalconduction in a predetermined path. The formation of these lesions bysoft tissue coagulation (also referred to as “ablation”) can provide thesame therapeutic benefits that the complex incision patterns that thesurgical maze procedure presently provides, but without invasive, openheart surgery.

Catheters used to create lesions typically include a relatively long andrelatively flexible body portion that has a soft tissue coagulationelectrode on its distal end and/or a series of spaced tissue coagulationelectrodes near the distal end. The portion of the catheter body portionthat is inserted into the patient is typically from 23 to 55 inches inlength and there may be another 8 to 15 inches, including a handle,outside the patient. The length and flexibility of the catheter bodyallow the catheter to be inserted into a main vein or artery (typicallythe femoral artery), directed into the interior of the heart, and thenmanipulated such that the coagulation electrode contacts the tissue thatis to be ablated. Fluoroscopic imaging is used to provide the physicianwith a visual indication of the location of the catheter.

In some instances, the proximal end of the catheter body is connected toa handle that includes steering controls. Exemplary catheters of thistype are disclosed in U.S. Pat. No. 5,582,609. In other instances, thecatheter body is inserted into the patient through a sheath and thedistal portion of the catheter is bent into loop that extends outwardlyfrom the sheath. This may be accomplished by pivotably securing thedistal end of the catheter to the distal end of the sheath, as isillustrated in co-pending U.S. application Ser. No. 08/769,856, filedDec. 19, 1996, and entitled “Loop Structures for Supporting MultipleElectrode Elements.” The loop is formed as the catheter is pushed in thedistal direction. The loop may also be formed by securing a pull wire tothe distal end of the catheter that extends back through the sheath, asis illustrated in U.S. Pat. No. 5,910,129, which is incorporated hereinby reference. Loop catheters are advantageous in that they tend toconform to different tissue contours and geometries and provide intimatecontact between the spaced tissue coagulation electrodes (or otherdiagnostic or therapeutic elements) and the tissue.

Mapping baskets, which may be carried on the distal end of separatemapping catheters, are often used to locate the reentry pathways priorto the formation of lesions. Exemplary mapping baskets are disclosed inU.S. Pat. No. 5,823,189. Additionally, once the lesions have beenformed, the mapping baskets are again used to determine whether thelesions have successfully eliminated the reentry pathways. Mappingbaskets are superior to conventional diagnostic catheters becausemapping baskets do not need to be steered to a variety of sites within abodily region such as the pulmonary vein during a diagnostic procedureand, instead, can perform a diagnostic procedure in a single beat from asingle location.

The use of a mapping catheter in combination with a soft tissuecoagulation catheter can, however, be problematic. For example, when amapping catheter is used in combination a soft tissue coagulationcatheter, a pair of transseptal punctures (or a single relatively largepuncture) must be formed in the atrial septum so that the catheters canbe advanced from the right atria, through the fossa ovalis and into theleft atria. Two punctures (or a relatively large single puncture) mustalso be formed in the femoral vein. In addition, the time required tomanipulate two catheters into their respective positions can lead toprolonged periods of fluoroscopy.

The issues associated with the combined use of mapping and coagulationcatheters notwithstanding, one lesion that has proven to be difficult toform with conventional catheters is the circumferential lesion that isused to isolate the pulmonary vein and cure ectopic atrial fibrillation.Lesions that isolate the pulmonary vein may be formed within thepulmonary vein itself or in the tissue surrounding the pulmonary vein.Conventional steerable catheters and loop catheters have proven to beless than effective with respect to the formation of suchcircumferential lesions. Specifically, it is difficult to form aneffective circumferential lesion by forming a pattern of relativelysmall diameter lesions.

Accordingly, the inventors herein have determined that a need exists fora device that is capable of both mapping and coagulating tissue. Theinventors herein have further determined that a need exists generallyfor structures that can be used to create circumferential lesions withinor around bodily orifices. The inventors herein have also determinedthat a need exists for a device that can both map the pulmonary vein andcreate lesions within or around the pulmonary vein.

SUMMARY OF THE INVENTION

Accordingly, the general object of the present inventions is to providea device that avoids, for practical purposes, the aforementionedproblems. In particular, one object of the present inventions is toprovide a device that can be used to create circumferential lesions inor around the pulmonary vein and other bodily orifices in a moreefficient manner than conventional apparatus. Another object of thepresent invention is to provide a device that can be used to both mapthe pulmonary vein and create lesions within or around the pulmonaryvein.

In order to accomplish some of these and other objectives, a probe inaccordance with one embodiment of a present invention includes a supportbody, an expandable/collapsible tissue coagulation structure supportedon the support body, and a mapping structure. The mapping structure maybe supported on the support body distally of the expandable/collapsibletissue coagulation structure or, alternatively, passable through a lumenin the support body so that it can be advanced beyond the distal end ofthe support body. Such a probe provides a number of advantages overconventional apparatus. For example, the combination of the tissuecoagulation structure and the mapping structure allows the physician toperform a mapping and coagulation procedure with a single instrument,thereby eliminating the aforementioned problems in the art. The mappingstructure may also be positioned within the pulmonary vein or otherorifice during a coagulation procedure and serve as an anchor to improvethe accuracy of the placement of the coagulation structure.Additionally, the expandable tissue coagulation structure is especiallyuseful for creating circular lesions in and around the pulmonary veinand other body orifices.

In order to accomplish some of these and other objectives, a probe inaccordance with one embodiment of a present invention includes a supportbody defining a longitudinal axis, an expandable/collapsible hoopstructure defining an open interior region and supported on the supportbody, at least one operative element supported on theexpandable/collapsible hoop structure. Such a probe provides a number ofadvantages over conventional apparatus. For example, in animplementation where the operative element consists of a plurality ofspaced electrodes, the hoop structure can be readily positioned suchthat the electrodes are brought into contact with tissue in or aroundthe pulmonary vein or other bodily orifice. The hoop structure alsodefines an open region that allows blood or other bodily fluids to passtherethrough. As a result, the present probe facilitates the formationof a circumferential lesion without the difficulties associated withconventional apparatus and does so without the occlusion of blood orother fluids.

The above described and many other features and attendant advantages ofthe present inventions will become apparent as the inventions becomebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed description of preferred embodiments of the inventions will bemade with reference to the accompanying drawings.

FIG. 1 is a side cutaway view of a probe in accordance with a preferredembodiment of a present invention.

FIG. 2 is a section view taken along line 2-2 in FIG. 1.

FIG. 3 is a side view of the probe illustrated in FIG. 1 in combinationwith a probe that supports a mapping basket.

FIG. 3 a is a side view of a probe similar to the probe illustrated inFIG. 1 with an integral mapping basket.

FIG. 4 is a side view of a probe in accordance with a preferredembodiment of a present invention.

FIG. 5 is a cutaway view of a portion of the probe illustrated in FIG.4.

FIG. 6 is a side view of a porous electrode illustrated in FIG. 4 withfold lines added thereto.

FIG. 6 a is a side view of a probe similar to the probe illustrated inFIG. 4 with the mapping basket mounted on a separate probe.

FIG. 7 is a side view of a probe in accordance with a preferredembodiment of a present invention.

FIG. 8 is a partial side view of the probe illustrated in FIG. 7 in acollapsed orientation.

FIG. 9 is a partial perspective view of a portion of the probeillustrated in FIG. 7.

FIG. 10 is a side, partial section view of the probe handle illustratedin FIG. 7.

FIG. 11 is a side view of the probe illustrated in FIG. 7 in combinationwith a probe that supports a mapping basket.

FIG. 11 a is a side view of a probe similar to the probe illustrated inFIG. 7 with an integral mapping basket.

FIG. 12 is a side view of a probe in accordance with a preferredembodiment of a present invention.

FIG. 13 is a partial perspective view of a portion of the probeillustrated in FIG. 12.

FIG. 14 is a side view of the probe illustrated in FIG. 12 in acollapsed orientation.

FIG. 14 a is a side view of the probe illustrated in FIG. 12 incombination with a probe that supports a mapping basket.

FIG. 14 b is a side view of a probe similar to the probe illustrated inFIG. 12 with an integral mapping basket.

FIG. 15 is a side view of a probe in accordance with a preferredembodiment of a present invention.

FIG. 16 is a perspective view of a probe in accordance with a preferredembodiment of a present invention.

FIG. 17 is an exploded perspective view showing certain elements in theprobe illustrated in FIG. 16.

FIG. 18 is perspective view of one of the structural members that formsthe hoop structure illustrated in FIGS. 16 and 17.

FIG. 19 is a perspective view of a probe in accordance with a preferredembodiment of a present invention.

FIG. 20 is a perspective view of a probe in accordance with a preferredembodiment of a present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the best presently knownmodes of carrying out the inventions. This description is not to betaken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the inventions.

The detailed description of the preferred embodiments is organized asfollows:

-   -   I. Introduction    -   II. Inflatable Structures    -   III. Hoop Structures    -   IV. Hoop Structure Electrodes, Temperature Sensing and Power        Control

The section titles and overall organization of the present detaileddescription are for the purpose of convenience only and are not intendedto limit the present inventions.

I. Introduction

The present inventions may be used within body lumens, chambers orcavities for diagnostic or therapeutic purposes in those instance whereaccess to interior bodily regions is obtained through, for example, thevascular system or alimentary canal and without complex invasivesurgical procedures. For example, the inventions herein have applicationin the diagnosis and treatment of arrhythmia conditions within theheart. The inventions herein also have application in the diagnosis ortreatment of ailments of the gastrointestinal tract, prostrate, brain,gall bladder, uterus, and other regions of the body.

With regard to the treatment of conditions within the heart, the presentinventions are designed to produce intimate tissue contact with targetsubstrates associated with various arrhythmias, namely atrialfibrillation, atrial flutter, and ventricular tachycardia. For example,the distal portion of a catheter in accordance with a present invention,which may include diagnostic and/or soft tissue coagulation electrodes,can be used to create lesions within or around the pulmonary vein totreat ectopic atrial fibrillation.

The structures are also adaptable for use with probes other thancatheter-based probes. For example, the structures disclosed herein maybe used in conjunction with hand held surgical devices (or “surgicalprobes”). The distal end of a surgical probe may be placed directly incontact with the targeted tissue area by a physician during a surgicalprocedure, such as open heart surgery. Here, access may be obtained byway of a thoracotomy, median stemotomy, or thoracostomy. Exemplarysurgical probes are disclosed in co-pending U.S. application Ser. No.09/072,872, filed May 5, 1998, and entitled “Surgical Methods andApparatus for Positioning a Diagnostic or Therapeutic Element Within theBody.”

Surgical probe devices in accordance with the present inventionspreferably include a handle, a relatively short shaft, and one of thedistal assemblies described hereafter in the catheter context.Preferably, the length of the shaft is about 4 inches to about 18inches. This is relatively short in comparison to the portion of acatheter body that is inserted into the patient (typically from 23 to 55inches in length) and the additional body portion that remains outsidethe patient. The shaft is also relatively stiff. In other words, theshaft is either rigid, malleable, or somewhat flexible. A rigid shaftcannot be bent. A malleable shaft is a shaft that can be readily bent bythe physician to a desired shape, without springing back when released,so that it will remain in that shape during the surgical procedure.Thus, the stiffness of a malleable shaft must be low enough to allow theshaft to be bent, but high enough to resist bending when the forcesassociated with a surgical procedure are applied to the shaft. Asomewhat flexible shaft will bend and spring back when released.However, the force required to bend the shaft must be substantial.

II. Inflatable Structures

As illustrated for example in FIGS. 1 and 2, a catheter 10 in accordancewith a preferred embodiment of a present invention includes a flexiblecatheter body 12 that may be formed from a biocompatible thermoplasticmaterial such as braided or unbraided Pebax® (polyether block emide),polyethylene, or polyurethane, and is preferably about 5 French to about9 French in diameter. Preferably, the catheter body 12 will have a twopart construction consisting of a relatively short flexible distalmember (formed from unbraided Pebax®) and a longer less flexibleproximal member (formed from braided Pebax®). The proximal and distalmembers may be bonded together with an overlapping thermal bond oradhesive bonded together end to end over a sleeve in what is referred toas a “butt bond.” The proximal end of the catheter body 12 is secured toa handle 14. An expandable (and collapsible) coagulation body 16 ismounted near the distal end of the catheter body 12. As described below,the expandable coagulation body 16 may be heated to a temperature thatwill cause soft tissue in contact with the coagulation body tocoagulate.

The expandable coagulation body 16, which is bonded to and disposedaround the catheter body 12, can be inflated with water, hypertonicsaline solution, or other biocompatible fluids. The fluid is suppliedunder pressure to the catheter 10 through an infusion/ventilation port18. The pressurized fluid travels to and from the expandable coagulationbody 16 through a fluid lumen 20 in the catheter body 12 and an aperture22 located within the expandable coagulation body. Pressure ismaintained to maintain the expandable coagulation body 16 in theexpanded orientation illustrated in FIG. 1. The pressure should berelatively low (less than 5 psi) and will vary in accordance with thedesired level of inflation, strength of materials used and the desireddegree of body flexibility. The fluid may be removed from the expandablecoagulation body 16 by applying a suction force to theinfusion/ventilation port 18.

For applications associated with the creation of lesions in or aroundthe pulmonary vein, the exemplary expandable coagulation body 16 ispreferably located about 3 cm to about 5 cm from the distal tip of thecatheter body 12 and the diameter is between about 2 mm and about 6 mmin the collapsed state and between about 10 mm and about 30 mm in theexpanded (or inflated) state. Suitable materials for the expandablecoagulation body 16 include relatively elastic thermally conductivebiocompatible materials such as silicone and polyisoprene. Other lesselastic materials, such as Nylon®, Pebax®, polyethylene and polyester,may also be used. Here, the expandable coagulation body will have to beformed with fold lines. [Note the discussion below concerning fold lineswith respect to the exemplary embodiment illustrated in FIG. 6.]Additionally, although the exemplary expandable coagulation body 16 hasa spherical shape, other shapes, such as a tear drop shape, acylindrical shape, or a prolate ellipsoid, may also be employed.

A fluid heating element is located within the expandable coagulationbody 16. In the preferred embodiment illustrated in FIGS. 1 and 2, thefluid heating element is an electrode 24 that is mounted on the catheterbody 12. Alternatively, a bi-polar pair of electrodes may be used totransmit power through a conductive fluid, such as the aforementionedisotonic saline solution, to generate heat. The temperature of the fluidmay be heated to about 90° C., thereby raising the temperature of theexterior of the expandable coagulation body 16 to approximately the sametemperature for tissue coagulation. The electrode may be formed frommetals such as platinum, gold and stainless steel.

The expandable coagulation body 16 tends to produce relativelysuperficial lesions. As such, it is especially useful for creatinglesions within the pulmonary vein.

The temperature of the fluid is preferably monitored for power controlpurposes. To that end, a temperature sensing element, such as theillustrated thermocouple 26, may mounted on the catheter body 12 withinthe expandable coagulation body 16. A reference thermocouple 28 may bepositioned near the distal end of the catheter body 12. Alternatively, athermistor or other temperature sensing element may be used in place ofthe thermocouple and reference thermocouple arrangement. The electrode24, thermocouple 26 and reference thermocouple 28 are respectivelyconnected to an electrical connector 30 by electrical conductors 32, 34and 36 which extend through a conductor lumen 38 in the catheter body.The connector 30 may be connected to a suitable RF power supply andcontrol apparatus.

The exemplary catheter body 12 illustrated in FIGS. 1 and 2 alsoincludes a central lumen 40 that is associated with a central port 42.The purpose of the central lumen is essentially two-fold. The centrallumen 40 serves as a guidewire lumen when the probe 10 is being directedto a bodily region of interest such as the pulmonary vein. A guidewire44 is first directed into the bodily region in conventional fashion andthe probe 10 is then advanced over the guidewire. A relatively shortintroducer sheath may be used to facilitate insertion of the catheter 10into the vasculature. Alternatively, a sheath which extends to theanatomical region of interest may be used. Once the probe reaches thebodily region of interest, the guidewire 44 may be removed so that thelumen can be used for its other purpose, which is to provide a passageto the bodily region for another device.

As illustrated for example in FIG. 3, a conventional basket catheter 46,such as the Constellation® basket catheter manufactured by EPTechnologies, Inc. in San Jose, Calif., may be advanced through thecentral lumen 40. The exemplary basket catheter 46 includes an elongatecatheter body 48, a mapping and/or coagulation basket 50 and ahandle/electrical connector 52. The basket may include two to eightelectrode supporting splines 54 and one to eight electrodes 56 on eachspline. The splines 54, which are preferably made of a resilient,biologically inert material such as Nitinol® metal, stainless steel orsilicone rubber, may be arranged either symmetrically or asymmetricallyabout the longitudinal axis of the basket 50. The splines 54 areconnected between a base member 58 and an end cap 60 in a resilient,pretensed, radially expanded condition, to bend and conform to theendocardial tissue surface they contact.

The exemplary basket 50 illustrated in FIG. 3, which is intended to beinserted into the pulmonary vein for pacing and mapping thereof,includes four splines 54 that respectively support two electrodes 56.The basket 50 also has a substantially elliptical shape and is betweenabout 20 mm and about 40 mm in diameter in its expanded state and about5 cm in length. Additional details concerning basket structures aredisclosed in U.S. Pat. No. 5,823,189, which is incorporated herein byreference.

The combination of the exemplary catheter 10 and basket catheter 46allows the physician to perform mapping and coagulation procedure with asingle instrument, thereby eliminating the aforementioned problems inthe art. Moreover, the basket 50 may be positioned within the pulmonaryvein or other orifice during a coagulation procedure and serve as ananchor to improve the accuracy of the placement of the expandablecoagulation body 16. In those instances where the basket is not present,the distal portion of the catheter body can serve as the anchor.

Another exemplary catheter in accordance a present invention isillustrated in FIGS. 4-6 and generally represented by reference numeral62. Catheter 62 is in many ways similar to the catheter illustrated inFIGS. 1-3 and like elements are represented with the like referencenumerals. There are, however, two primary differences. Catheter 62includes an expandable (and collapsible) porous electrode structure 64,as opposed to the heated expandable coagulation body 16, and theelectrode supporting basket 50 is mounted on the distal portion of thecatheter body 12, as opposed to being mounted on a separate catheterthat is advanced through the central lumen 40.

As shown by way of example in FIG. 5, the expandable porous electrode64, which is formed from an electrically non-conductive thermoplastic orelastomeric material, includes a porous region 66 having pores 68 andtwo non-porous regions 70 and 72. The pores 68, which are actuallymicropores, are shown diagrammatically in enlarged form for the purposeof illustration. Liquid pressure is used to inflate the expandableporous electrode 64 and maintain it in its expanded state. The liquid,which is supplied through the infusion/ventilation port 18 and fluidlumen 20 (FIG. 2), enters the expandable porous electrode 64 by way ofthe aperture 22. The expandable porous electrode 64 will then expandfrom its collapsed, low profile state (between about 2.3 mm and about5.3 mm in diameter) to its expanded state (between about 10 mm and about30 mm).

An electrode 24 formed from material with both relatively highelectrical conductivity and relatively high thermal conductivity iscarried within the expandable porous electrode 64. Suitable materialsinclude gold, platinum, and platinum/iridium. Noble metals arepreferred. Here too, the electrode 24, thermocouple 26 and referencethermocouple 28 are connected to the electrical connector 30 byelectrical conductors 32, 34 and 36 which extend through conductor lumen38 in the catheter body 12 (note FIG. 2). The liquid used to fill theexpandable porous electrode 64 is an electrically conductive liquid thatestablishes an electrically conductive path to convey RF energy from theelectrode 24 to tissue.

The pores 68 establish ionic transport of the tissue coagulating energyfrom the electrode 24 through the electrically conductive fluid totissue outside the porous electrode 64. The liquid preferably possessesa low resistivity to decrease ohmic loses, and thus ohmic heatingeffects, within the porous electrode 64. The composition of theelectrically conductive liquid can vary. A hypertonic saline solution,having a sodium chloride concentration at or near saturation, which isabout 20% weight by volume is preferred. Hypertonic saline solution hasa low resistivity of only about 5 ohm•cm, compared to blood resistivityof about 150 ohm•cm and myocardial tissue resistivity of about 500ohm•cm. Alternatively, the fluid can be a hypertonic potassium chloridesolution. This medium, while promoting the desired ionic transfer,requires closer monitoring of the rate at which ionic transport occursthrough the pores 68, to prevent potassium overload. When hypertonicpotassium chloride solution is used, it is preferred keep the ionictransport rate below about 1 mEq/min.

Ionic contrast solution, which has an inherently low resistivity, can bemixed with the hypertonic sodium or potassium chloride solution. Themixture enables radiographic identification of the porous electrode 64without diminishing the ionic transfer through the pores 68.

Due largely to mass concentration differentials across the pores 68,ions in the conductive fluid will pass into the pores because ofconcentration differential-driven diffusion. Ion diffusion through thepores 68 will continue as long as a concentration gradient is maintainedacross the porous electrode 64. The ions contained in the pores 68provide the means to conduct current across the porous electrode 64.When RF energy is conveyed from a RF power supply and control apparatusto the electrode 24, electric current is carried by the ions within thepores 68. The RF currents provided by the ions result in no netdiffusion of ions, as would occur if a DC voltage were applied, althoughthe ions do move slightly back and forth during the RF frequencyapplication. This ionic movement (and current flow) in response to theapplied RF field does not require perfusion of liquid through the pores68. The ions convey RF energy through the pores 68 into tissue to areturn electrode, which is typically an external patch electrode(forming a unipolar arrangement). Alternatively, the transmitted energycan pass through tissue to an adjacent electrode (forming a bipolararrangement). The RF energy heats tissue (mostly ohmically) to coagulatethe tissue and form a lesion.

The preferred geometry of the expandable porous electrode 64 isessentially tear drop-shaped and symmetric with a ring of pores 68surrounded by non-porous regions. The ring is preferably about 2 mm toabout 10 mm wide. This porous electrode configuration is especiallyuseful for forming relatively deep lesions around the entrance to thepulmonary vein. However, nonsymmetrical or non tear drop-shapedgeometries can be used. The porous electrode may, for example, be formedwith a spherical shape. Elongated, cylindrical geometries can also beused. The distal non-porous region 72 may be eliminated and replacedwith a porous region. The shape and size of the porous region 66 mayalso be varied.

With respect to materials, the porous region 66 of the expandable porouselectrode 64 is preferably formed from regenerated cellulose or amicroporous elastic polymer. Hydroscopic materials with microporescreated through the use of lasers, electrostatic discharge, ion beambombardment or other processes may also be used. The non-porous regionsare preferably formed from relatively elastic materials such as siliconeand polyisoprene. However, other less elastic materials, such as Nylon®,Pebax®, polyethylene, polyesterurethane and polyester, may also be used.Here, the expandable porous electrode 64 may be provided with creasedregions 74 that facilitate the collapse of the porous electrode, as isillustrated for example in FIG. 6. A hydrophilic coating may be appliedto the non-porous regions to facilitate movement of the porous electrode64 in to and out of a sheath.

Like the exemplary catheter 10 illustrated in FIGS. 1-3, exemplarycatheter 62 may be directed to the anatomical site of interest, such asthe pulmonary vein, by advancing the catheter through a relatively shortintroducer sheath and over a guidewire 44. However, because the basket50 is mounted on the distal end of the catheter, the base member 58 andend cap 60 are provided with apertures through which the guidewire 44extends. A relatively short introducer sheath may be used to facilitateinsertion of the catheter 62 into the vasculature or, alternatively, asheath which extends to the anatomical region of interest may be used.

It should be noted that the exemplary catheter 10 illustrated in FIGS.1-3 may be provided with a basket that is fixedly mounted on the distalend of the catheter body 12. Such a catheter is identified by referencenumeral 10′ in FIG. 3 a. Similarly, the basket may be removed from thecatheter 62 illustrated in FIGS. 4-6 so that a separate basket cathetermay be used in combination therewith in a manner similar to thatillustrated in FIG. 3. Such a catheter is identified by referencenumeral 46′ in FIG. 6 a.

Additional information and examples of expandable and collapsible bodiesare disclosed in U.S. patent application Ser. No. 08/984,414, entitled“Devices and Methods for Creating Lesions in Endocardial and SurroundingTissue to Isolate Arrhythmia Substrates,” U.S. Pat. No. 5,368,591, andU.S. Pat. No. 5,961,513, each of which is incorporated herein byreference.

III. Hoop Structures

As illustrated for example in FIGS. 7-10, a catheter 76 in accordancewith an invention herein includes a catheter body 78 that supports acollapsible hoop structure 80 at or near its distal end. The hoopstructure 80 may be used to support one or more operative elements incontact with an annular tissue region such as the pulmonary vein. Forexample, the hoop structure 80 may be used to support a plurality ofspaced electrodes 82. The exemplary collapsible hoop structure 80includes a substantially circular hoop spline 84, a pair of distalsupport splines 86 and a pair of proximal support splines 88. The shapeof the hoop spline 84 may, alternatively, be oval, elliptical or anyother two or three-dimensional shape required for a particularapplication. The end of each of the support splines 86 and 88 includes aloop 89 that encircles the corresponding portion of the hoop spline 84in the manner illustrated in FIG. 9. Excessive movement of the supportsplines 86 and 88 around the circumference of the hoop spline 84 isprevented by the electrodes 82.

The exemplary collapsible hoop structure 80 may be driven from theexpanded orientation illustrated in FIG. 7 to the collapsed orientationillustrated in FIG. 8 by moving the distal support splines 86 andproximal support splines 88 away from one another. In the illustratedembodiment, the catheter body 78 is configured to move the proximal anddistal support splines 86 and 88 in this manner. More specifically, thecatheter body 78 includes a pair of catheter body members 90 and 92 thatare movable relative to one another. The catheter body members 90 and 92are preferably tubular members arranged such that member 92 is slidablyreceived within the lumen of member 90. The distal support splines 86are secured to the catheter body member 90, while the proximal supportsplines 88 are secured to the catheter body member 92. When the catheterbody member 92 is moved proximally relative to the catheter body member90, the distal and proximal support splines 86 and 88 will be moved awayfrom one another to collapse the hoop structure 80. Relative movement inthe opposite direction will expand the support structure. Of course, thecatheter body member 92 may be moved relative to the catheter bodymember 90, or both catheter body members may be moved, in otherimplementations of the invention.

In the exemplary embodiment illustrated in FIGS. 7-10, the distal andproximal support splines 86 and 88 are secured to the catheter bodymembers 90 and 92 with anchor rings 94 and 96. The distal and proximalsupport splines 86 and 88 are preferably spot welded to the anchor rings94 and 96 and the anchor rings are preferably glued to the catheter bodymembers 90 and 92. Other methods of attachment may also be used.

The hoop spline 84, distal support splines 86 and proximal supportsplines 88 are preferably made of a resilient, biologically inertmaterial such as Nitinol® metal, stainless steel or an elastic polymer(e.g. silicone rubber). The splines are preshaped into theconfigurations corresponding to an expanded hoop structure 80. In animplementation suitable for pulmonary vein applications, the hoop spline84 will be about 10 mm to about 30 mm in diameter. The catheter bodymembers 90 and 92 may be formed from a biocompatible thermoplasticmaterial such as braided or unbraided Pebax®, polyethylene, orpolyurethane. In an implementation suitable for pulmonary veinapplications, the catheter body member 90 will have an outer diameter ofabout 1.5 mm and an inner diameter of about 1 mm, while the catheterbody member 92 will have an outer diameter of about 2.2 mm and an innerdiameter of about 1.6 mm.

The splines are preferably covered with tubes formed from abiocompatible polymer material such as Pebax®) or Nylon®. Conductorwires (not shown) for the electrodes 82 and temperature sensors 83(discussed in Section IV below) pass through the tubes and into thelumen of the catheter body member 90.

The exemplary catheter 76 also includes a handle 98 capable of movingthe catheter body members 90 and 92 relative to one another. Referringmore specifically to FIG. 10, the exemplary handle 98 includes a handlebody 100 with a suitable electrical connector (not shown) for theconductor wires from the electrodes 82 and temperature sensors 83, apiston 102 that is slidably mounted in a longitudinally extendingaperture in the handle body, and a thumb rest 104. The handle body 100,piston 102 and thumb rest 104 are preferably formed from machined ormolded plastic. The catheter body member 92 is secured to a strainrelief element 105 on the thumb rest 104 with an adhesive or othersuitable instrumentality. The catheter body member 90 extends throughthe catheter body member 92, through a lumen formed in the piston 102and into the proximal portion of the handle body 100. The catheter bodymember 90 is glued or otherwise secured to an anchor 106 which is itselfheld in place by a set screw 108 or other suitable device. As theposition of the catheter body member 90 is fixed relative to the handle100 and the piston 102 and proximal catheter body member 92 are notfixed relative to the handle, the catheter body member 92 may be movedrelative to the catheter body member 90 by moving the piston.

In order to insure that the piston 102 in the exemplary handle 98illustrated in FIGS. 7, 8 and 10 does not move once it has been placedin the position corresponding to a collapsed hoop structure 80, a setscrew 110 engages a key way 112 formed in the piston. The friction forcebetween the set screw 110 and key way 112 is sufficient to overcome theforce generated by a collapsed hoop structure 80. Additionally, thelongitudinal edges of the piston key way 112 limit the range of motionof the piston 102 by engaging the set screw 110. In the preferredembodiment, the length of the key way 112 is approximately 0.75 inch,but can range from approximately 0.375 inch to approximately 1.5 inches.Additionally, although the preferred embodiment includes theabove-described set screw and key way arrangement, other mechanisms forapplying a friction force to the piston and limiting its range of motionmay also be employed. For example, fluting to limit the range of pistonmotion, a tapered collet, o-rings in addition to those discussed below,or a circumferential piston grip may be used in place of the preferredscrew and key way arrangement.

The exemplary handle 98 also includes a compression spring 114 thatapplies a distally directed biasing force to the piston 102. The biasingforce reduces the amount of force that must be applied to the piston 102by the physician to move the piston in the distal direction and expandthe hoop structure 80. The compression spring 114 is located between theproximal end of the piston 102 and an annularly shaped abutment 116.Because of the biasing force imparted to the piston 102 by thecompression spring 114, the amount of physician-generated actuationforce required to drive the piston is reduced.

A pair of o-rings 118 may be used to center the piston 102 within thehandle body 100 of the exemplary handle 98. The o-rings 118 also preventthe piston from canting. The side of the exemplary piston 102 oppositethe key way 112 includes a pair of Teflon® rods 120 which ride on thesurface of the longitudinally extending aperture in the handle body 100.The Teflon® rods 120 provide improved lubricity and prevent the setscrew 110 from driving the piston 102 into the surface of the aperture.

The exemplary catheter 76 may be advanced over a guidewire 122 (locatedwithin the inner lumen of the catheter body member 90) into the bodilyregion of interest in conventional fashion. A relatively shortintroducer sheath or a sheath which extends to the anatomical region ofinterest may be used if desired. The hoop structure 80 can then beexpanded and used to create an annular lesion at the entrance to orwithin, for example, the pulmonary vein. Additionally, because theelectrodes 82 or other operative elements are mounted on a hoop spline84, tissue coagulation can be achieved without occluding blood flow.

The inner lumen of the catheter body member 90 may also be used toprovide a passage to the bodily region for another device. Asillustrated for example in FIG. 11, a conventional basket catheter 124,such as the Constellation® basket catheter manufactured by EPTechnologies, Inc. in San Jose, Calif., may be advanced through thelumen of the distal catheter member 90. The basket catheter 124 may beadvanced over the guidewire 122, as shown, or the guidewire may beremoved from the lumen in the catheter body member prior to insertion ofthe basket catheter.

The exemplary basket catheter 124 includes an elongate catheter body126, a mapping and/or coagulation basket 128 and a handle/electricalconnector (not shown). Like the basket 50 described above with referenceto FIG. 3, the exemplary basket 128 includes four symmetrically arrangedsplines 129, which are preferably made of a resilient, biologicallyinert material such as Nitinol® metal, stainless steel or siliconerubber. Each spline 129 supports two electrodes 130 and is supported ina resilient, pretensed, radially expanded condition between a basemember 132 and an end cap 134. Basket catheter 124 is configured for usewithin the pulmonary vein and has a substantially elliptical shape andis between about 20 mm and about 40 mm in diameter in its expanded stateand about 5 cm in length in the collapsed state. Nevertheless, thenumber of splines and electrodes on each spline, as well as the overallsize of the basket 128, may be increased or decreased as applicationsrequire.

The combined catheter 76 and basket catheter 124 allows the physician toperform mapping and coagulation procedure with a single instrument,thereby eliminating the aforementioned problems in the art. The basketcan also be used as an anchor to improve the accuracy of the placementof the hoop structure 80.

As illustrated for example in FIG. 11 a, a catheter 76′, which isotherwise identical to catheter 76, may include a basket 128′ that isintegral with distal end of the catheter body member 90. Here, thehandle 100 would also include a suitable electrical connector for thebasket 128′.

Another exemplary catheter including a collapsible hoop structure, whichis generally represented by reference numeral 136, is illustrated inFIGS. 12-14. The catheter includes a catheter body 138 that supports acollapsible hoop structure 140. The hoop structure 140 may be used tosupport one or more operative elements in contact with an annular tissueregion such as the pulmonary vein. For example, the hoop structure 140may be used to support a plurality of spaced electrodes 142. Theexemplary hoop structure 140 includes a substantially circular hoopspline 144 and four radially extending support splines 146. The shape ofthe hoop spline 144 may, alternatively, be oval, elliptical or any othershape required for a particular application. The support splines 146 arewelded or otherwise secured to an anchor ring 147 that is mounted on thecatheter body 138. The anchor ring 147 may be held in place with aninterference fit, adhesive, or a combination thereof.

A first pair of stylets 148 a and 0.148 b and a second pair of stylets150 a and 150 b are attached to the exemplary hoop spline 144. The endssupport splines 146 and stylets 148 a, 148 b, 150 a and 150 b includerespective loops 152 that encircle the corresponding portion of the hoopspline 144 in the manner illustrated in FIG. 13. The stylets 148 a, 148b and 150 a, 150 b extend into a lumen within the catheter body 138through apertures 154 and are wound into respective stylet pairs 148 and150.

The catheter body 138 and support splines 146 may be formed from thesame materials as their counterparts in the preferred embodimentillustrated in FIGS. 7-11. In particular, the support splines 146 arepreferably formed from Nitinol® metal, stainless steel or an elasticpolymer, and the anchor ring 147 should be formed from the same materialas the support splines. The stylets 148 a, 148 b, 150 a and 150 b may beformed from inert wire such as Nitinol® or 17-7 stainless steel wire.The catheter body also includes lumens for the stylets, electricalconductors associated with the electrodes and temperature sensors, and aguidewire.

The exemplary catheter 136 also includes a handle 156. The wound styletpairs 148 and 150 pass through handle apertures 158 and 160 and theproximal ends of the stylet pairs may be provided with grips 162 and164. The exemplary hoop structure 140 may be driven from the expandedorientation illustrated in FIG. 12 to the collapsed orientationillustrated in FIG. 14 by moving the stylet pair 148 (and stylets 148 aand 148 b) in the distal direction and moving the stylet pair 150 (andstylets 150 a and 150 b) in the proximal direction. Alternatively, thehandle may be provided with conventional bi-directional steeringapparatus, such as the rotatable knob arrangement illustrated in U.S.Pat. No. 5,254,088 or the rotatable gear and rack arrangementillustrated in U.S. Pat. No. 5,364,351, to drive the stylet pairs 148and 150 in opposite directions. In any event, the handle 156 preferablyalso includes an electrical connector 166.

The exemplary catheter 136 may be advanced over a guidewire that passesthrough a lumen in the catheter body member 138. A relatively shortintroducer sheath or a sheath which extends to the anatomical region ofinterest may be used if desired. Here too, the hoop structure 140 canthen be expanded and used to create an annular lesion without occludingblood flow.

The exemplary catheter illustrated in FIGS. 12-14 may also be used inconjunction with a mapping basket. As illustrated for example in FIG. 14a, a basket catheter 124 such as that illustrated in FIG. 11 may beadvanced through the guidewire lumen of catheter 136. Alternatively, asillustrated for example in FIG. 14 b, a modified catheter 136′ includesa basket 128′ mounted on the distal end of the catheter body 138.

Other types of lesion creating catheters may be provided with anintegral mapping basket. As illustrated for example in FIG. 15,exemplary catheter 168 includes a proximal portion 170, a helical distalportion 172 and an integral mapping/coagulation basket 174. The helicaldistal portion 172 preferably supports a plurality of electrodes 176.The number of revolutions, length, diameter and shape of the helicalportion 172 will vary from application to application. The helicalportion illustrated in FIG. 15, which may be used to create lesions inor around the pulmonary vein, revolves around the longitudinal axis ofthe catheter 168 one and one-half times in its relaxed state. The basket174, which is essentially the same as those described above, includesfour splines 178 and a pair of electrodes 180 on each spline. Otherbasket configurations may be used as applications so require.

The exemplary catheter 168 also includes a stylet 182 that enables thephysician to manipulate the helical distal portion 172 and adjust itsshape. The distal portion of the stylet 182 is fixedly secured withinthe region of the catheter distal of the helical distal portion 172. Thestylet 182 can be moved distally and proximally and can also be rotatedin one direction, which will cause the helical portion of unwind so thatits diameter decreases, or rotated in the other direction to cause itsdiameter to decrease. In any of these states, the helical portion willdefine an open area interior to the electrodes 176 through which bloodor other bodily fluids can flow. As a result, the helical portion can beused to create a circumferential lesion in or around the pulmonary vein,or other bodily orifice, without occluding fluid flow.

The exemplary catheter 168 illustrated in FIG. 15 is not a steerablecatheter and, accordingly, may be advanced though a conventionalsteerable guide sheath to the target location. The sheath should belubricious to reduce friction during movement of the catheter 168. Priorto advancing the catheter 168 into the sheath, the stylet 182 will bemoved to and held in its distal most position in order to straighten outthe helical distal portion 172. The stylet 182 will remain in thisposition until the helical distal portion 172 is advanced beyond thedistal end of the sheath. A sheath introducer, such as those used incombination with basket catheters, may be used when introducing thecatheter into the sheath.

Additional information concerning the helical catheter illustrated inFIG. 15, albeit without the mapping basket, is disclosed in concurrentlyfiled and commonly assigned U.S. application Ser. No. ______, which isentitled “Loop Structures For Supporting Diagnostic and TherapeuticElements in Contact With Body Tissue” and incorporated herein byreference.

Another exemplary catheter with a hoop structure is illustrated in FIGS.16-18. Referring first to FIG. 16, the catheter 184 includes a catheterbody 186 and a collapsible hoop structure 188 at the distal end thereof.The hoop structure 188 may be used to support one or more operativeelements, such as the illustrated electrodes 190, in contact with anannular tissue region such as the pulmonary vein. The exemplary hoopstructure 188 includes a substantially circular hoop spline 192 and foursupport splines 194. The hoop spline 192 may also be oval, elliptical orany other shape, and the number of support splines 194 may be increasedor decreased, as applications require. In an implementation suitable forpulmonary vein applications, the hoop spline 192 will be about 10 mm toabout 30 mm in diameter.

As illustrated for example in FIGS. 17 and 18, the exemplary hoopstructure 188 is composed of four substantially identical structuralmembers 196, each of which consists of a pair of struts 198 and a curvedportion 200 that extends approximately ninety degrees, and four moldedtubes 202 that extend outwardly from the catheter body 186. One strut198 from each of two adjacent structural members 196 is inserted into atube 202. To that end, the struts 198 are formed with bends 204 so thatthe struts will conform to the shape of the region 206 that includes thedistal portion of the catheter body 186 and the tubes 202 that extendoutwardly therefrom. Each support spline 194 is, therefore, a compositestructure consisting of two struts 198 and a molded tube 202. Wiringfrom the electrodes 190 and temperature sensors associated with theelectrodes (not shown) will pass through the tubes 202 and into a lumenextending through the catheter body 186.

The structural members 196 are preferably formed from a resilient,biologically inert material such as Nitinol® metal, stainless steel orsilicone rubber that is preshaped into the configuration correspondingto an expanded hoop structure 188. The catheter body 186 and moldedtubes 202 may be formed from a biocompatible thermoplastic material suchas braided or unbraided Pebax®, polyethylene, or polyurethane.

A relatively short introducer sheath and, preferably, a sheath whichextends to the anatomical region of interest will be used in conjunctionwith the exemplary catheter illustrated in FIGS. 16-18. Here too, thehoop structure can be expanded and used to create an annular lesion atthe entrance to or within, for example, the pulmonary vein withoutoccluding blood flow.

As illustrated for example in FIG. 19, the exemplary hoop structure 188illustrated in FIGS. 16-18 can be reconfigured slightly in order toincrease the collapsibility of the structure. The exemplary hoopstructure 188′ is essentially identical to hoop structure 188 but forthe configuration of the structural members 196. Here, the curvedportions 200′ in hoop structure 188′ are rotated distally in thedirection of the arrows “A” relative to the curved portions 200 in hoopstructure 188 to increase the collapsibility.

Still another exemplary hoop structure is illustrated in FIG. 20 andgenerally represented by reference numeral 208. Here, the catheter isprovided with a catheter body 210 and a collapsible hoop structure 212at the distal end thereof. The hoop structure 212 may be used to supportone or more operative elements, such as the illustrated electrodes 214,in contact with an annular tissue region such as the pulmonary vein. Theexemplary hoop structure 212 includes a substantially circular hoopspline 216, four proximal support splines 218, four distal supportsplines 220, a base 222 and an end cap 224. In addition to providingadditional structural support, the distal support splines 220 act as ananchor during tissue coagulation procedures. The hoop spline 214 will beabout 10 mm to about 30 mm in diameter in implementations suitable forpulmonary vein applications. The hoop spline 216 may also be oval,elliptical or any other shape, and the number of support splines 218,220 may be increased or decreased, as applications require.

IV. Hoop Structure Electrodes, Temperature Sensing and Power Control

In each of the preferred embodiments, the operative elements are aplurality of spaced electrodes. However, other operative elements, suchas lumens for chemical ablation, laser arrays, ultrasonic transducers,microwave electrodes, and resistive heating wires, and such devices maybe substituted for the electrodes. Additionally, although electrodes andtemperature sensors are discussed below in the context of the exemplarycatheter described with reference to FIGS. 7-11, the discussion is alsoapplicable to the exemplary catheters described with reference to FIGS.12-20.

The spaced electrodes 82 are preferably in the form of wound, spiralcoils. The coils are made of electrically conducting material, likecopper alloy, platinum, or stainless steel, or compositions such asdrawn-filled tubing (e.g. a copper core with a platinum jacket). Theelectrically conducting material of the coils can be further coated withplatinum-iridium or gold to improve its conduction properties andbiocompatibility. A preferred coil electrode is disclosed in U.S. Pat.No. 5,797,905. The electrodes 82 are electrically coupled to individualwires (such as those illustrated in FIG. 2) to conduct coagulatingenergy to them. The wires are passed in conventional fashion through alumen extending through the associated catheter body into a PC board inthe catheter handle, where they are electrically coupled to a connectorthat is received in a port on the handle. The connector plugs into asource of RF coagulation energy.

As an alternative, the electrodes may be in the form of solid rings ofconductive material, like platinum, or can comprise a conductivematerial, like platinum-iridium or gold, coated upon the device usingconventional coating techniques or an ion beam assisted deposition(IBAD) process. For better adherence, an undercoating of nickel ortitanium can be applied. The electrodes can also be in the form ofhelical ribbons. The electrodes can also be formed with a conductive inkcompound that is pad printed onto a non-conductive tubular body. Apreferred conductive ink compound is a silver-based flexible adhesiveconductive ink (polyurethane binder), however other metal-based adhesiveconductive inks such as platinum-based, gold-based, copper-based, etc.,may also be used to form electrodes. Such inks are more flexible thanepoxy-based inks.

The flexible electrodes 82 are preferably about 4 mm to about 20 mm inlength. In the preferred embodiment, the electrodes are 12.5 mm inlength with 1 mm to 3 mm spacing, which will result in the creation ofcontinuous lesion patterns in tissue when coagulation energy is appliedsimultaneously to adjacent electrodes. For rigid electrodes, the lengthof the each electrode can vary from about 2 mm to about 10 mm. Usingmultiple rigid electrodes longer than about 10 mm each adversely effectsthe overall flexibility of the device, while electrodes having lengthsof less than about 2 mm do not consistently form the desired continuouslesion patterns.

The portion of the electrodes that are not intended to contact tissue(and be exposed to the blood pool) may be masked through a variety oftechniques with a material that is preferably electrically and thermallyinsulating. This prevents the transmission of coagulation energydirectly into the blood pool and directs the energy directly toward andinto the tissue. For example, a layer of UV adhesive (or anotheradhesive) may be painted on preselected portions of the electrodes toinsulate the portions of the electrodes not intended to contact tissue.Deposition techniques may also be implemented to position a conductivesurface only on those portions of the assembly intended to contacttissue. Alternatively, a coating may be formed by dipping the electrodesin PTFE material.

The electrodes may be operated in a uni-polar mode, in which the softtissue coagulation energy emitted by the electrodes is returned throughan indifferent patch electrode (not shown) externally attached to theskin of the patient. Alternatively, the electrodes may be operated in abi-polar mode, in which energy emitted by one or more electrodes isreturned through other electrodes. The amount of power required tocoagulate tissue ranges from 5 to 150 w.

As illustrated for example in FIG. 9, a plurality of temperature sensors83, such as thermocouples or thermistors, may be located on, under,abutting the longitudinal end edges of, or in between, the electrodes82. Preferably, the temperature sensors 83 are located at thelongitudinal edges of the electrodes 82 on the distally facing side ofthe hoop or helical structure. In some embodiments, a referencethermocouple (not shown) may also be provided. For temperature controlpurposes, signals from the temperature sensors are transmitted to thesource of coagulation energy by way of wires (such as those illustratedin FIG. 2) that are also connected to the aforementioned PC board in thecatheter handle. Suitable temperature sensors and controllers whichcontrol power to electrodes based on a sensed temperature are disclosedin U.S. Pat. Nos. 5,456,682, 5,582,609 and 5,755,715.

Finally, the electrodes 82 and temperature sensors 83 can include aporous material coating, which transmits coagulation energy through anelectrified ionic medium. For example, as disclosed in U.S. applicationSer. No. 08/879,343, filed Jun. 20, 1997, entitled “Surface Coatings ForCatheters, Direct Contacting Diagnostic and Therapeutic Devices,”electrodes and temperature sensors may be coated with regeneratedcellulose, hydrogel or plastic having electrically conductivecomponents. With respect to regenerated cellulose, the coating acts as amechanical barrier between the surgical device components, such aselectrodes, preventing ingress of blood cells, infectious agents, suchas viruses and bacteria, and large biological molecules such asproteins, while providing electrical contact to the human body. Theregenerated cellulose coating also acts as a biocompatible barrierbetween the device components and the human body, whereby the componentscan now be made from materials that are somewhat toxic (such as silveror copper).

Although the present inventions have been described in terms of thepreferred embodiments above, numerous modifications and/or additions tothe above-described preferred embodiments would be readily apparent toone skilled in the art. It is intended that the scope of the presentinventions extend to all such modifications and/or additions and thatthe scope of the present inventions is limited solely by the claims setforth below.

1-29. (canceled)
 30. A mapping and coagulation apparatus, comprising: atissue coagulation probe including a tissue coagulation probe supportbody defining at least one interior lumen, a hoop structure supported onthe tissue coagulation probe support body, and at least one operativeelement supported on the hoop structure; and a mapping probe passablethrough the tissue coagulation probe support body lumen including amapping probe support body, and a mapping structure supported on themapping probe support body.
 31. A mapping and coagulation apparatus asclaimed in claim 30, wherein the tissue coagulation probe support bodydefines a longitudinal axis and the hoop structure defines a planeperpendicular to the longitudinal axis.
 32. A mapping and coagulationapparatus as claimed in claim 30, wherein the hoop structure comprises ahoop spline and at least first and second support splines.
 33. A mappingand coagulation apparatus as claimed in claim 32, wherein the hoopstructure collapses in response to movement of the first and secondsupport splines in opposite directions.
 34. A mapping and coagulationapparatus as claimed in claim 33, wherein the tissue coagulation probesupport body comprises a first support body member defining an innerlumen and a second support body member movable within the inner lumen ofthe first support body member and defining the at least one interiorlumen, the first support spline is operably connected to the firstsupport body member, and the second support spline is operably connectedto the second support body member.
 35. A mapping and coagulationapparatus as claimed in claim 30, wherein the hoop structure comprises ahoop spline, a plurality of support splines, and first and secondproximally extending stylets.
 36. A mapping and coagulation apparatus asclaimed in claim 35, wherein the hoop structure collapses in response tomovement of the first and second stylets in opposite directions.
 37. Amapping and coagulation apparatus as claimed in claim 30, wherein thehoop structure comprises a helical support structure.
 38. A mapping andcoagulation apparatus as claimed in claim 30, wherein the at least oneoperative element comprises a plurality of spaced electrodes. 39.(canceled)
 40. (canceled)
 41. A probe, comprising: a support bodydefining a longitudinal axis; an expandable/collapsible hoop structuredefining an open interior region and supported on the support body suchthat the longitudinal axis of the support body passes through the openinterior region; and at least one operative element supported on theexpandable/collapsible hoop structure.
 42. A probe as claimed in claim41, wherein the support body comprises a catheter.
 43. A probe asclaimed in claim 41, wherein the at one operative element comprises aplurality of spaced electrodes.
 44. A probe as claimed in claim 41,wherein the hoop structure comprises a hoop spline and at least firstand second support splines.
 45. A probe as claimed in claim 44, whereinthe hoop structure collapses in response to movement of the first andsecond support splines in opposite directions.
 46. A probe as claimed inclaim 45, wherein the support body comprises a first support body memberdefining an inner lumen and a second support body member movable withinthe inner lumen, the first support spline is operably connected to thefirst support body member, and the second support spline is operablyconnected to the second support body member.
 47. A probe as claimed inclaim 41, wherein the hoop structure comprises a hoop spline, aplurality of support splines, and first and second proximally extendingstylets.
 48. A probe as claimed in claim 47, wherein the hoop structurecollapses in response to movement of the first and second stylets inopposite directions.
 49. A probe as claimed in claim 41, wherein thehoop structure comprises a helical support structure.
 50. A probe asclaimed in claim 41, wherein the hoop structure comprises a hoop splineand at least first and second radially extending support splines.
 51. Aprobe as claimed in claim 41, wherein the hoop structure comprises ahoop spline and at least first and second distally extending supportsplines that respectively define acute angles with the longitudinal axisof the support body.
 52. A probe as claimed in claim 51, wherein thesupport body includes tubular members extending distally therefrom atthe acute angle and the support splines are at least partially locatedwithin the tubular members.
 53. A probe as claimed in claim 51, whereinthe first and second support splines extend distally from the supportbody to the hoop spline and the hoop structure further includes at leastthird and fourth support splines extending distally from the hoopspline.
 54. A probe as claimed in claim 41, wherein the hoop structurecomprises at least two structural members, each structural memberconsisting of a pair of struts and a curved portion.
 55. A probe asclaimed in claim 54, wherein the hoop structure comprises fourstructural members.
 56. A probe as claimed in claim 41, wherein thesupport body defines a distal end and the hoop structure is locatedproximally of the distal end of the support body.
 57. A probe as claimedin claim 41, wherein the support body defines a distal end and the hoopstructure extends distally from the distal end of the support body.